Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753827AbbFRIqL (ORCPT ); Thu, 18 Jun 2015 04:46:11 -0400 Received: from us01smtprelay-2.synopsys.com ([198.182.47.9]:58294 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752727AbbFRIqF (ORCPT ); Thu, 18 Jun 2015 04:46:05 -0400 Message-ID: <55828527.8050901@synopsys.com> Date: Thu, 18 Jun 2015 14:15:27 +0530 From: Vineet Gupta User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 Newsgroups: gmane.linux.kernel.cross-arch,gmane.linux.kernel To: Michal Marek , Geert Uytterhoeven CC: "linux-arch@vger.kernel.org" , lkml Subject: Re: subtle side effect of commit a1c48bb160f836 References: <55826966.6050202@synopsys.com> <20150618081329.GA9434@pobox.suse.cz> In-Reply-To: <20150618081329.GA9434@pobox.suse.cz> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.12.197.3] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2482 Lines: 67 On Thursday 18 June 2015 01:43 PM, Michal Marek wrote: >> > Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE, >> > a(nother) Kconfig option may make sense. > We can also introduce some ARCH_CFLAGS that is appended near the end of > the list, and have arc/Makefile add its -O3 there. But I'd like to why > the -O3 needs to be there in first place. This is how historically ARC kernels have been built. We do track performance results LMBench/hackbench... and going from -O3 to -O2 caused a sudden dip in some of the numbers when we measured 3.18 (vs. 3.13) > Obviously, the kernel works > with -O2, otherwise the regression would have been identified earlier. Its a performance thing - so yeah -O2 works, but -O3 works even better :-) > So why can't users specify -O3 in KCFLAGS like on any other > architecture. Sweet, I didn't know about this. But I don't see any arch setting this - only tile using it. So yeah - below does the trick ! ---------> >From 5e44cd2ed69b1d030b4cb87600d2767b69c35537 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Thu, 18 Jun 2015 13:54:01 +0530 Subject: [PATCH] ARC: Override toplevel default -O2 with -O3 ARC kernels have historically been built with -O3, despite top level Makefile defaulting to -O2. This was facilitated by implicitly ordering of arch makefile include AFTER top level assigned -O2. An upstream fix to top level a1c48bb160f ("Makefile: Fix unrecognized cross-compiler command line options") changed the ordering, making ARC -O3 defunt. Fix that by NOT relying on any ordering whatsoever and use the right mechanism to do the over-rides. Suggested-by: Michal Marek Cc: Geert Uytterhoeven Cc: Signed-off-by: Vineet Gupta --- arch/arc/Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arc/Makefile b/arch/arc/Makefile index 86c71b2089d2..c23f3f2b0ff8 100644 --- a/arch/arc/Makefile +++ b/arch/arc/Makefile @@ -44,6 +44,7 @@ endif ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE # Generic build system uses -O2, we want -O3 cflags-y += -O3 +KCFLAGS += -O3 endif # small data is default for elf32 tool-chain. If not usable, disable it -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/